1. Field of the Invention
The present invention relates to a suspension system for a vehicle and, more particularly, to a suspension system which can improve controllability and stability of the vehicle and ride comfort by automatically controlling a height of a roll center in accordance the vehicle's running conditions.
2. Description of Related Art
The primary functions of a suspension system are to (1) provide vertical compliance so wheels can follow an uneven road, thereby isolating a vehicle body from roughness in the road, (2) maintain the wheels in proper steer and camber attitudes with respect to the road surface, (3) react to control forces produced by tires-longitudinal acceleration and braking forces, lateral force, and braking and driving torques, (4) resist roll of the vehicle body, and (5) keep the tires in contact with the road with minimal load variations.
Particularly, the roll occurs on the basis of a predetermined point, called a roll center, when the vehicle is cornering. The variation rate of the roll center's height has an effect on the running safety and handling safety of the vehicle.
That is, rolling of the vehicle occurs when the height of a gravitational center of the vehicle body becomes higher than that of the roll center. If lowering the height of the roll center, it is easy to optimize the camber and tread changes such that the vibration from the road can be minimized to improve the high speed straight running performance and safety as well as the ride comfort.
However, when lateral force is induced to the vehicle body during cornering, the vehicle body's behavior becomes cumbersome and deteriorates the handling safety.
On the contrary, if raising the height of the roll center, a resistance against the roll is increased, whereby a shorter anti-roll bar can be used. However, the camber and tread changes becomes large such that the ride comfort and the straight running safety are deteriorated.
Accordingly, it is very important to optimally set the height of the roll center by compromising between the two characteristics when designing the suspension system.